Spinel-rich metasomatized CAI from Kaidun

Details Spinel-rich metasomatized CAI from Kaidun Spinel-rich metasomatized CAI from Kaidun

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29r.542u&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 542-543

Mathematics

Logic

Chemical Composition, Chondrites, Inclusions, Meteoritic Composition, Spinel, Temperature Effects, Breccia, Isotopic Enrichment, Mineralogy, Solar Corona, Textures

Scientific paper

The Kaidun meteorite is a heterogeneous breccia that contains a set of components of different composition and history. Here we present the results of a study of an unusual Ca, Al-rich Inclusions (CAI) that was found in a polished section of a C3-type breccia sample. The CAI has the outline of keyhole and consists of a round part (A) with a diameter approximately 70 microns and an elongated part (B). The longest dimension of the object is approximately 210 microns. A comparison of the CAI and matrix compositions shows an enrichment of the former in refractory and volatile elements. High contents of refractory elements in the CAI may be explained by the high-temperature nature of the proto-CAI. A similar alteration process is likely to be responsible for the Fe and Zn contents of the spinel and the presence of ilmenite. The texture and the mineralogical and chemical compositions of the CAI reflect a complex history. The two parts of the compound CAI must have formed separately with different primary mineral associations of the cores but a similar diopsidic rim. Both parts experienced intensive metasomatic alterations with part B having been exposed to a vapor with fractionated Na/K ratio. Part B broke and was twisted before it met part A and became attached to it. Finally both became part of the chondritic rock. The fact that the two parts developed very different Na/K ratios in their groundmasses makes it unlikely that they were metasomatized within the same parcel of vapor or within the rock after accretion. This compound CAI clearly excludes in-situ metasomatic alteration and demonstrates the mobility of objects in and the chemical inhomogeneity of the solar nebula.

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